For older people with presbyopia, changing glasses for different activities can prevent falls. Although multifocal glasses are helpful for activities that require changes in focal length, they impair depth perception and have been shown to increase the risk of tripping and falling. Sydney researchers performed a randomised trial over 13 months among elderly regular wearers of multifocal glasses, in which the intervention group swapped to using single lens distance glasses for activities outside their own home such as walking, going up and down stairs and covering uneven ground. They found only a modest 8% reduction in falls in the intervention group overall, but a much larger (40%) reduction in a subgroup who usually engaged in regular outdoor activities. However, for those who did not normally take part in outdoor activities, the change in glasses significantly increased their risk of an outdoor fall. The authors of a linked editorial cautioned that any changes to glasses in the elderly involve careful instruction, and should be introduced gradually so that the person is not overwhelmed.